Liquid ejection apparatus and method for manufacturing liquid ejection apparatus

ABSTRACT

A liquid ejection apparatus is disclosed. One apparatus includes a piezoelectric element. The piezoelectric element includes an upper electrode and a lower electrode. The lower electrode has a partial overlapping portion and a non-overlapping portion. The partial overlapping portion at least partially overlaps the pressure chamber. The partial overlapping portion of the lower electrode has two ends in the transverse direction. The upper electrode has two ends in the transverse direction. A distance from the center of the pressure chamber in the transverse direction to one of the two ends of the upper electrode in the transverse direction is smaller than a distance from the center of the pressure chamber in the transverse direction to a corresponding one of the two ends of the partial overlapping portion in the transverse direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No.2015-192764 filed on Sep. 30, 2015, the content of which is incorporatedherein by reference in its entirety.

FIELD OF DISCLOSURE

The disclosure relates to a liquid ejection apparatus and a method formanufacturing the liquid ejection apparatus.

BACKGROUND

A known liquid ejection apparatus, e.g., an inkjet head, is configuredto eject ink from nozzles thereof. The inkjet head includes a channeledsubstrate including a plurality of pressure chambers and a piezoelectricactuator provided on the channeled substrate. Each of the pressurechambers of the channeled substrate communicates with a correspondingone of the nozzles and has a rectangular shape. In other words, each ofthe pressure chambers has a longitudinal direction. The pressurechambers are arranged along a transverse direction orthogonal to thelongitudinal direction.

The piezoelectric actuator includes a vibration plate and a plurality ofpiezoelectric elements. The vibration plate is formed of, for example,silicon dioxide, and covers the pressure chambers. The piezoelectricelements are provided on the vibration plate in correspondence with thepressure chambers. Each of the piezoelectric elements includes apiezoelectric film, a lower electrode located below the piezoelectricfilm, and an upper electrode located above the piezoelectric film.

The lower electrode is an individual electrode individually provided foreach pressure chamber. The lower electrode is disposed on the vibrationplate, overlapping a central portion of the pressure chamber in itstransverse direction. The upper electrode is disposed overlapping almostthe entire area of the pressure chamber with respect to its transversedirection. The upper electrodes are electrically connected to each otherbetween the piezoelectric elements, and the same potential is applied tothe upper electrodes. The upper electrodes constitute a common electrodeshared among the piezoelectric elements.

A portion of the piezoelectric film between the lower electrode and theupper electrode is an active portion configured to deform when a voltageis applied between the two electrodes. As described above, the upperelectrode overlaps the almost entire area of the pressure chamber withrespect to its transverse direction. Accordingly, a position of each endof the active portion with respect to the transverse direction isdetermined by a position of a corresponding end of the lower electrode.

SUMMARY

In the liquid ejection apparatus, the lower electrode is disposed on anupper surface of the vibration plate, overlapping the central portion ofthe pressure chamber with respect to the transverse direction. In otherwords, in a region of the upper surface of the vibration plateoverlapping the pressure chamber with respect to its transversedirection, the lower electrode is disposed at a central portion of theregion, but is not at end portions of the region. Therefore, a portionof the piezoelectric film is formed on the lower electrode at thecentral portion of the region, but other portions of the piezoelectricfilm is formed directly on the vibration plate at the end portions ofthe region.

The crystal growth of piezoelectric material may differ between caseswhere the piezoelectric film is formed directly on the vibration plateincluding, for example, silicon dioxide, e.g., an amorphous layer, andwhere the piezoelectric film is formed on the lower electrode, e.g., acrystalline layer. Therefore, a portion of the piezoelectric film formedat the central portion of the region and the other portions of thepiezoelectric film formed at the end portions of the region may differwith respect to a crystal orientation direction. This may causediscontinuous crystallinity in piezoelectric film between the centralportion and the end portions of the region. Further, in the liquidejection apparatus, positions of ends of the active portion with respectto the transverse direction is determined by the lower electrode.Therefore, an end portion of the active portion may have discontinuouscrystallinity. Therefore, when a voltage is applied to the piezoelectricelement to deform the active portion, non-uniform distortion may occurat the end portion of the active portion where crystallinity isdiscontinuous. This may cause a crack in the piezoelectric film, and theelement may be damaged.

One or more aspects of the disclosure are to realize a structure thatreduces discontinuous crystallinity of a piezoelectric material at anend portion of an active portion including a piezoelectric film formedof the piezoelectric material, and to prevent or reduce occurrence of acrack in the piezoelectric film when the active portion deforms.

According to an aspect of the disclosure, a liquid ejection apparatusincludes a pressure chamber having a longitudinal direction. The liquidejection apparatus includes a first insulating film covering thepressure chamber. The liquid ejection apparatus includes a piezoelectricelement. The piezoelectric element corresponds to the pressure chamber.The piezoelectric element includes a lower electrode disposed above thefirst insulating film. The piezoelectric element includes apiezoelectric film disposed above the lower electrode. The piezoelectricelement includes an upper electrode disposed above the piezoelectricfilm. The liquid ejection apparatus includes a common trace connectingto the upper electrode and another upper electrode. The upper electrodeand the another upper electrode are disposed side by side in atransverse direction. The transverse direction is orthogonal to thelongitudinal direction. The lower electrode has a partial overlappingportion and a non-overlapping portion. The partial overlapping portionat least partially overlaps the pressure chamber in an orthogonaldirection. The orthogonal direction is orthogonal to the longitudinaldirection and the transverse direction. The partial overlapping portionof the lower electrode has two ends in the transverse direction. Theupper electrode has two ends in the transverse direction. A distancefrom the center of the pressure chamber in the transverse direction toone of the two ends of the upper electrode in the transverse directionis smaller than a distance from the center of the pressure chamber inthe transverse direction to a corresponding one of the two ends of thepartial overlapping portion in the transverse direction.

According to an aspect of the disclosure, a method for manufacturing aliquid ejection apparatus includes forming a first insulating film overa substrate, forming a lower electrode having two ends thereof inparticular direction over the first insulating film, forming apiezoelectric film over the lower electrode, and forming a upperelectrode and common trace over the piezoelectric film. The upperelectrode having two ends thereof in the particular direction. Thecommon trace connects to the upper electrode and another upperelectrode. A distance from a center of the upper electrode in theparticular direction to one of the two ends of the upper electrode inthe particular direction is smaller than a distance from the center ofthe lower electrode in the particular direction to a corresponding oneof the two ends of the lower electrode in the particular direction.

According to an aspect of the disclosure, a liquid ejection apparatusincludes a pressure chamber having a longitudinal direction aninsulating film covering the pressure chamber and a piezoelectricelement corresponding to the pressure chamber. The piezoelectric elementincludes a lower electrode disposed above the insulating film, apiezoelectric film disposed above the lower electrode, and an upperelectrode disposed above the piezoelectric film. The liquid ejectionapparatus includes a common trace connecting to the upper electrode andanother upper electrode. The lower electrode has two ends in atransverse direction. The transverse direction is orthogonal to thelongitudinal direction. The two ends of the lower electrode are locatedon opposite sides of a center of the pressure chamber in the transversedirection. The upper electrode has two ends in the transverse direction.The two ends of the upper electrode are located on opposite sides of thecenter of the pressure chamber in the transverse direction. As viewedalong a centerline of the pressure chamber extending in the transversedirection, a distance from the center of the pressure chamber in thetransverse direction to one of the two ends of the upper electrode inthe transverse direction is smaller than a distance from the center ofthe pressure chamber in the transverse direction to a corresponding oneof the two ends of the lower electrode in the transverse direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a printer in an illustrativeembodiment according to one or more aspects of the disclosure.

FIG. 2 is a plan view of a head unit.

FIG. 3 is an enlarged view of a portion A in FIG. 2.

FIG. 4 is an enlarged view of the portion A from which an insulatingfilm, an individual trace, and a thick trace depicted in FIG. 3 areremoved.

FIG. 5A is a cross-sectional view taken along a line V-V in FIG. 3. FIG.5B is a cross-sectional view taken along a line V-V in FIG. 3, whereinFIG. 5B shows one modification of illustrative embodiment.

FIG. 6 is a cross-sectional view taken along a line VI-VI in FIG. 3.

FIGS. 7A-7E depict manufacturing processes of the head unit, whereinFIG. 7A depicts a process of forming the insulating film; FIG. 7Bdepicts a process of forming a lower electrode; FIG. 7C depicts aprocess of forming a piezoelectric film; FIG. 7D depicts a process offorming an upper electrode; and FIG. 7E depicts a process of forming apiezoelectric film for protecting the insulating film.

FIGS. 8A and 8B depict manufacturing processes of the head unit, whereinFIG. 8A depicts a process of forming pressure chambers; and FIG. 8Bdepicts a process of bonding a nozzle plate.

FIGS. 9A and 9B are cross-sectional views of a head unit according to amodification of the illustrative embodiment, wherein FIGS. 9A and 9Bcorrespond to FIG. 6.

FIG. 10 is a cross-sectional view of a head unit according to anothermodification of the illustrative embodiment, wherein FIG. 10 correspondsto FIG. 6.

FIG. 11 is a cross-sectional view of a head unit according to yetanother modification of the illustrative embodiment, wherein FIG. 11corresponds to FIG. 5A.

FIG. 12 is a cross-sectional view of a head unit according to stillanother modification of the illustrative embodiment, wherein FIG. 12corresponds to FIG. 5A.

FIG. 13 is a cross-sectional view of a head unit according to still yetanother modification of the illustrative embodiment, wherein FIG. 13corresponds to FIG. 5A.

DETAILED DESCRIPTION

An illustrative embodiment of the disclosure will be described. FIG. 1is a plan view of a printer in an illustrative embodiment according toone or more aspects of the disclosure. Referring to FIG. 1, generalstructures of an inkjet printer 1 will be described. The front, rear,left, and right sides of the printer 1 are defined as depicted inFIG. 1. The front or near side and the back side of the sheet of FIG. 1are defined as the top/upper side and the bottom/lower side of theprinter 1, respectively. Hereinafter, description will be made withreference to directions as defined above.

(General Structures of Printer)

As depicted in FIG. 1, the inkjet printer 1 includes a platen 2, acarriage 3, an inkjet head 4, a feeding mechanism 5, and a controller 6.

A recording medium, e.g., a recording sheet 100, is placed on an uppersurface of the platen 2. The carriage 3 is configured to reciprocatealong two guide rails 10 and 11 in the left-right direction (which maybe referred to as the scanning direction hereinafter) at a regionopposing the platen 2. An endless belt 14 is connected to the carriage3. A carriage drive motor 15 drives the endless belt 14 to move thecarriage 3 in the scanning direction.

The inkjet head 4 is mounted on the carriage 3. The inkjet head 4 isconfigured to move together with the carriage 3 in the scanningdirection. The inkjet head 4 includes four head units 16 aligned in thescanning direction. The four head units 16 are connected by tubes (notdepicted) to a cartridge holder 7 on which ink cartridges 17 of fourcolors (e.g., black, yellow, cyan, and magenta) are mounted. Each of thehead units 16 has a plurality of nozzles 24 (refer to FIGS. 2-6) formedon a lower surface thereof (e.g., the back side of the sheet of FIG. 1).The nozzles 24 of the respective head units 16 are configured to ejectink supplied from the corresponding ink cartridges 17, toward therecording sheet 100 placed on the platen 2.

The feeding mechanism 5 includes two feeding rollers 18 and 19sandwiching the platen 2 therebetween in the front-rear direction. Thefeeding mechanism 5 is configured to feed the recording sheet 100 placedon the platen 2 with the feeding rollers 18 and 19 in a frontwarddirection (which may be referred to as the feeding directionhereinafter).

The controller 6 includes a read only memory (ROM), a random accessmemory (RAM), and an application specific integrated circuit (ASIC)including various control circuits. The controller 6 is configured toexecute various processing, e.g., printing onto the recording sheet 100,based on programs stored in the ROM, with the ASIC. For example, inprint processing, the controller 6 controls the inkjet head 4 and thecarriage drive motor 15 to print, for example, an image, on therecording sheet 100, based on a print command input from an externaldevice, e.g., a personal computer (PC). More specifically, an inkejection operation and a feeding operation are alternately performed. Inthe ink ejection operation, ink is ejected while the inkjet head 4 ismoved together with the carriage 3 in the scanning direction. In thefeeding operation, the recording sheet 100 is fed in the feedingdirection by a predetermined amount by the feeding rollers 18 and 19.

(Details of Inkjet Head)

Next, structures of the four head units 16 of the inkjet head 4 will bedescribed in detail. The four head units 16 have the same or similarstructures, so that one of the head units 16 will be described below.

FIG. 2 is a plan view of the head unit 16. FIG. 3 is an enlarged view ofa portion A in FIG. 2. FIG. 4 is an enlarged view of the portion A fromwhich an insulating film 40, an individual trace 41, and a thick trace44 depicted in FIG. 3 are removed. FIG. 5A is a cross-sectional viewtaken along a line V-V in FIG. 3. FIG. 6 is a cross-sectional view takenalong a line VI-VI in FIG. 3. As depicted in FIGS. 2-6, the head unit 16includes a nozzle plate 20, a channeled substrate 21, a piezoelectricactuator 22, a Chip On Film (COF) 50, and a cover member 23. Forsimplicity of illustration, the cover member 23 disposed above thechanneled substrate 21 and the COF 50 are omitted in FIG. 2. In FIG. 3,the COF 50 is schematically shown by a two-dot chain line.

(Nozzle Plate)

The nozzle plate 20 is a plate formed of, for example, silicon. Thenozzle plate 20 has the nozzles 24 formed therein. As depicted in FIG.2, the nozzles 24 are arranged along the feeding direction. The nozzles24 constitute two nozzle rows 27 aligned in the scanning direction. Ineach nozzle row 27, the nozzles 24 are arranged in a pitch P. Positionsof the nozzles 24 of the two nozzle rows 27 are mutually deviated in thefeeding direction by a half of the pitch P (P/2).

(Channeled Substrate)

The channeled substrate 21 includes a silicon single crystal substrate.The channeled substrate 21 includes a plurality of pressure chambers 26communicating with the corresponding nozzles 24. Each of the pressurechambers 26 has a rectangular planar shape elongated in the scanningdirection. The pressure chambers 26 are arranged along the feedingdirection in accordance with the arrangement of the nozzles 24. Thepressure chambers 26 constitute two pressure chamber rows 28 arranged inthe scanning direction. A lower surface of the channeled substrate 21 iscovered by the nozzle plate 20. When viewed from the top-bottomdirection, an inner end portion of each pressure chamber 26 in thescanning direction, e.g., an end portion of the pressure chamber 26closer to the center of the channeled substrate 21 in the scanningdirection, overlaps a corresponding nozzle 24. In the description, “aninner side”, “an inner portion,” and “an inner end” in the scanningdirection may be used to describe a side, a portion, and an end closerto the center of the head unit 16 in the scanning direction,respectively.

As depicted in FIG. 2, two manifolds 25 are formed at left and right endportions of the channeled substrate 21 in correspondence with therespective pressure chamber rows 28. Each manifold 25 extends along thefeeding direction. As depicted in FIGS. 3-5, each of the pressurechambers 26, which constitute one pressure chamber row 28, is connectedto a corresponding manifold 25 by a corresponding throttle channel 29.The throttle channel 29 extends in the scanning direction.

The manifold 25 has an open end on an upper surface of the channeledsubstrate 21. An opening of the manifold 25 is connected to thecartridge holder 7 by an ink supply member (not depicted) including, forexample, the tubes. Ink in the ink cartridge 17 of the cartridge holder7 flows into the manifold 25 via the ink supply member. Then, the ink issupplied from the manifold 25 to the respective pressure chambers 26,via the corresponding throttle channels 29.

(Piezoelectric Actuator)

The piezoelectric actuator 22 is a laminated body including a pluralityof films. The piezoelectric actuator 22 includes an insulating film 30,a plurality of piezoelectric elements 31, the insulating film 40 forprotecting the piezoelectric elements 31, individual traces 41, and acommon trace 42. The piezoelectric actuator 22 is disposed on thechanneled substrate 21, covering the pressure chambers 26.

<Insulating Film 30>

The insulating film 30 is a silicon dioxide film formed by, for example,oxidizing a surface of the silicon channeled substrate 21. The thicknessof the insulating film 30 is, for example, 1.0-1.5 μm. Eachpiezoelectric element 31 is disposed at a portion of an upper surface ofthe insulating film 30 overlapping a corresponding one of the pressurechambers 26. The piezoelectric element 31 is configured to apply, to inkin the pressure chamber 26, ejection energy for ejecting ink from thecorresponding nozzle 24.

<Piezoelectric Elements 31>

Structures of the piezoelectric elements 31 will be described. Each ofthe piezoelectric elements 31 includes a lower electrode 32 disposedabove the insulating film 30, a piezoelectric film 33 disposed above thelower electrode 32, and an upper electrode 34 disposed above thepiezoelectric film 33.

The lower electrode 32 is disposed at a portion of the upper surface ofthe insulating film 30 overlapping the pressure chamber 26. The lowerelectrode 32 is a so-called individual electrode. An individual drivesignal is supplied from a driver IC 51 (described below) to theindividual electrode, e.g., the lower electrode 32, via thecorresponding individual trace 41. In a structure in which the lowerelectrode 32 on the insulating film 30 serves as the individualelectrode, a trace for supplying the drive signal to the lower electrode32 may be formed on the insulating film 30, which is flat. Accordingly,the trace may be readily formed and may not readily break.

The lower electrode 32 includes a wide portion 32 a and a narrow portion32 b. The wide portion 32 a is an example of a partial overlappingportion. The narrow portion 32 b is an example of a non-overlappingportion. The wide portion 32 a has a rectangular shape elongated in thescanning direction. The narrow portion 32 b is disposed on an inner sideof the piezoelectric actuator 22 in the scanning direction relative tothe wide portion 32 a. As depicted in FIGS. 3 and 5, the wide portion 32a is disposed overlapping a central portion of the pressure chamber 26in its longitudinal direction, e.g., the scanning direction. As depictedin FIGS. 3, and 6, each end of the wide portion 32 a with respect to thetransverse direction of the pressure chamber 26, e.g., the feedingdirection, is located further from a corresponding end of the pressurechamber 26 with respect to the feeding direction. In other words, thewide portion 32 a is partially located beyond an edge of the pressurechamber 26 with respect to the feeding direction. As depicted in FIG. 3,with respect to the feeding direction, the width of the narrow portion32 b is smaller than the width of the wide portion 32 a. The narrowportion 32 b is lead from an inner end portion of the wide portion 32 ain the scanning direction (e.g., a right end portion of the wide portion32 a in FIG. 3) and extends to a portion between the two pressurechamber rows 28. The lower electrode 32 includes, for example, platinum(Pt). The thickness of the lower electrode 32 is, for example, 0.1 μm.

The piezoelectric film 33 is formed of piezoelectric material, e.g.,lead zirconate titanate (PZT). In another embodiment, the piezoelectricfilm 33 may be formed of a lead-free piezoelectric material that doesnot include lead, instead of PZT. The thickness of the piezoelectricfilm 33 is, for example, 1.0-2.0 μm. More specifically, in theillustrative embodiment, the piezoelectric film 33 of the piezoelectricelements 31 is connected along the feeding direction, constituting apiezoelectric body 37. The piezoelectric body 37 has a rectangular shapeelongated along the feeding direction, as depicted in FIGS. 2 and 3. Inother words, two piezoelectric bodies 37 including the piezoelectricfilm 33 are disposed on the insulating film 30 in correspondence withthe two pressure chamber rows 28.

As depicted in FIG. 5A, the narrow portion 32 b of the lower electrode32 extends in the scanning direction toward the center of channeledsubstrate 21 beyond a side surface 33 a of the piezoelectric film 33.The side surface 33 a is provided at an inner side of the piezoelectricfilm 33 in the scanning direction (e.g., a right side of thepiezoelectric film 33 in FIG. 5A). The narrow portion 32 b includes afirst exposed portion 32 c exposed from the side surface 33 a andextending toward the center of channeled substrate 21 in the scanningdirection. The lower electrode 32 is connected to the individual trace41 (described below), via the first exposed portion 32 c of the narrowportion 32 b.

As depicted in FIGS. 2-4 and 6, a slit 38 is formed at a portion of thepiezoelectric body 37 between the pressure chambers 26. The slit 38extends in the scanning direction. The slit 38 is provided between twopressure chambers 26 that are adjacent along the feeding direction. Withthe slit 38, a portion of the piezoelectric film 33 corresponding to onepressure chamber 26 includes two side surfaces 33 b with respect to thefeeding direction, as depicted in FIG. 6. With respect to the feedingdirection, each end of the lower electrode 32 is located beyond acorresponding end of the pressure chamber 26, and a corresponding sidesurface 33 b of the piezoelectric film 33.

The upper electrode 34 is disposed at a portion of an upper surface ofthe piezoelectric film 33 overlapping the pressure chamber 26. The upperelectrode 34 has a rectangular planar shape elongated in the scanningdirection, similar to the wide portion 32 a of the lower electrode 32.The upper electrode 34 is formed of, for example, iridium. The thicknessof the upper electrode 34 is, for example, 0.1 μm.

As depicted in FIGS. 3 and 6, with respect to the transverse directionof the pressure chamber 26, e.g., the feeding direction, the width ofthe upper electrode 34 is smaller than the width of the wide portion 32a. With respect to the feeding direction, each end of the upperelectrode 34 is located closer to the center of the pressure chamber 26than a corresponding end of the lower electrode 32. The upper electrodes34 of the piezoelectric elements 31 are connected to each other by thecommon trace 42 (described below). A ground potential is applied to theupper electrodes 34.

The piezoelectric film 33 of each piezoelectric element 31 is sandwichedbetween the lower electrode 32 and the upper electrode 34 at a regionfacing the pressure chamber 26. A portion of the piezoelectric film 33sandwiched between the lower electrode 32 and the upper electrode 34 ishereinafter referred to as the active portion 36. In each piezoelectricelement 31, an electric field in a thickness direction of the activeportion 36 may be applied to active portion 36 due to a potentialdifference between the lower electrode 32 and the upper electrode 34.This may cause the active portion 36 to deform in its planar direction,e.g., a direction perpendicular to a thickness direction of the activeportion 36. In response to the deformation of the active portion 36, thepiezoelectric element 31 as a whole deforms. Accordingly, a portion ofthe piezoelectric element 31 facing the pressure chamber 26 deforms inthe top-bottom direction orthogonal to a planar direction of theinsulating film 30.

As described above, in the illustrative embodiment, with respect to thefeeding direction, each end of the upper electrode 34 is located closerto the center of the pressure chamber 26 than a corresponding end of thelower electrode 32, as depicted in FIG. 6. In other words, a position ofeach end of the active portion 36 with respect to the feeding directionis determined by a position of a corresponding end of the upperelectrode 34. The piezoelectric film 33 includes a central portion 33 xlocated closer to the center of the pressure chamber 26 with respect tothe feeding direction than the respective ends of the upper electrode 34with respect to the feeding direction. The piezoelectric film 33 furtherincludes an end portion 33 y located on an end portion thereof withrespect to the feeding direction. The central portion 33 x and the endportion 33 y are both formed above the lower electrode 32. Therefore, inthe central portion 33 x, which is a portion of the active portion 36,and the end portion 33 y, which is not a portion of the active portion36, crystals of the piezoelectric material is preferentially oriented toa predetermined plane, e.g., a (100) plane. More specifically, an endportion of the active portion 36 may not have discontinuouscrystallinity, which may prevent or reduce occurrence of a crack in thepiezoelectric film 33 when the active portion 36 deforms. The expression“preferentially oriented to a (100) plane” includes a case in which allof the crystals of the piezoelectric film 33 are oriented to the (100)plane and a case in which 90% or more of the crystals are oriented tothe (100) plane.

To preferentially orient the piezoelectric film 33 in a predeterminedplane, the lower electrode 32 preferably includes platinum (Pt).Platinum is oriented by itself regardless of conditions of an underlyingsubstrate. Platinum crystallizes into a face-centered cubic (FCC)lattice structure that is a close-packed structure. Therefore, theplatinum layer may be oriented to a predetermined plane direction evenon, for example, an amorphous silicon dioxide layer, e.g., theinsulating film 30. Accordingly, the piezoelectric film 33 formed on thelower electrode 32 whose crystal direction are aligned in one direction.In another embodiment, a seed layer may be provided between the lowerelectrode 32 and the piezoelectric film 33 to control crystal growth onthe piezoelectric film 33. A material for the seed layer may beappropriately selected from known materials, e.g., titanium oxide, leadtitanate, and PZT.

Especially, in the illustrative embodiment, each end of the lowerelectrode 32 with respect to the feeding direction is located beyond acorresponding end of the pressure chamber 26. The lower electrode 32 isprovided across the pressure chamber 26 with respect to the feedingdirection. Accordingly, discontinuous crystallinity may not readilyoccur at a region of the piezoelectric film 33 overlapping the pressurechamber 26.

The lower electrode 32 is formed extending beyond each end of thepressure chamber 26 with respect to the feeding direction. Therefore,the lower electrode 32 may prevent or reduce reduction in the thicknessof a portion of the insulating film 30 located below the piezoelectricfilm 33 and covering the pressure chamber 26, when the piezoelectricfilm 33, which is first entirely formed over the upper surface of theinsulating film 30, is etched to form the side surfaces 33 b.

With respect to the feeding direction, each end of the lower electrode32 is located beyond a corresponding one of the two side surfaces 33 bof the piezoelectric film 33. In other words, with respect to thefeeding direction, an entire portion of the piezoelectric film 33 isdisposed above the lower electrode 32. Accordingly, the piezoelectricfilm 33 may not have discontinuous crystallinity as described above.

As depicted in FIG. 5A, a conductive film 39 is located on a side of thepiezoelectric film 33 closer to the first exposed portion 32 c of thelower electrode 32. The conductive film 39 is formed of the samematerial as the upper electrodes 34 (e.g., iridium). The conductive film39 is provided at an end portion of the piezoelectric film 33 and thefirst exposed portion 32 c. The conductive film 39 extends from an uppersurface of the piezoelectric film 33 to an upper surface of the firstexposed portion 32 c, through the side surface 33 a of the piezoelectricfilm 33. The conductive film 39 is formed at the time of patterning theupper electrodes 34. As will be described later, a conductive film isformed throughout a surface of the piezoelectric film 33 and theconductive film is patterned by etching, to form the upper electrodes34. During the etching process, the conductive film 39 covering thefirst exposed portion 32 c is intentionally left, to prevent the firstexposed portion 32 c disposed below the conductive film 39 from beingetched.

<Insulating Film 40>

As described above, in the illustrative embodiment, with respect to thefeeding direction, the width of the upper electrode 34 is smaller thanthe width of the wide portion 32 a. Therefore, the upper electrode 34does not cover a portion of a surface of the piezoelectric film 33. Theinsulating film 40 is provided for protecting the piezoelectric film 33at the portion of the surface of the piezoelectric film 33 that is notcovered by the upper electrode 34. The insulating film 40 may prevent orreduce moisture from externally entering into the piezoelectric film 33.

More specifically, as depicted in FIGS. 3 and 5, the insulating film 40is provided on an upper surface of the piezoelectric film 33 of eachpiezoelectric element 31 around the upper electrode 34. The insulatingfilm 40 slightly overlaps a peripheral edge portion of the upperelectrode 34. In other words, in the upper surface of the piezoelectricfilm 33, a central portion of the upper electrode 34 is exposed from theinsulating film 40. Therefore, the insulating film 40 may not inhibitthe deformation of the active portion 36. The insulating film 40 coversthe side surface 33 a with respect to the scanning direction, and theside surfaces 33 b with respect to the feeding direction, from the uppersurface of the piezoelectric film 33.

As depicted in FIG. 5A, the insulating film 40 covers a portion of theconductive film 39 provided on an inner end portion (e.g., a right endportion in FIG. 5A) of the piezoelectric film 33 in the scanningdirection, but does not cover another portion, e.g., an inner endportion of the conductive film 39 in the scanning direction, provided onthe first exposed portion 32 c. The another portion is a second exposedportion 39 a exposed from the insulating film 40.

A portion of the piezoelectric film 33 overlapping an edge portion ofthe pressure chamber 26 may readily have a crack when the active portion36 deforms. However, in the illustrative embodiment, as depicted in FIG.5A, in an inner end portion of the piezoelectric film 33 in the scanningdirection (e.g., a right end portion in FIG. 5A), the insulating film 40covers an end portion of the upper electrode 34, and the side surface 33a of the piezoelectric film 33. An end E1 (e.g., a left end of a rightportion of the insulating film 40 in FIG. 5A) is located closer to thecenter of the pressure chamber 26 than an edge of the pressure chamber26. In other words, the insulating film 40 overlaps an edge portion ofthe pressure chamber 26 with respect to the scanning direction.Therefore, a curvature radius of a deformed shape of the piezoelectricfilm 33 may become relatively great at a position corresponding the edgeportion of the pressure chamber 26. Accordingly, a crack may beprevented or reduced. Further, the end E1 of the insulating film 40 islocated closer to the center of the pressure chamber 26 than an end of aregion B where the wide portion 32 a of the lower electrode 32 overlapsthe upper electrode 34 vertically. In short, the insulating film 40overlaps the active portion 36. Accordingly, a crack in thepiezoelectric film 33 may further be prevented or reduced.

Further, as depicted in FIG. 6, the insulating film 40 extends along thefeeding direction from an upper surface of the upper electrode 34 to anupper surface of the insulating film 30, via an upper surface of thepiezoelectric film 33 and the side surface 33 b. In other words, theinsulating film 40 covers end portions of the lower electrode 32, eachextending beyond a corresponding one of the two side surfaces 33 b ofthe piezoelectric film 33. Thus, a portion of the insulating film 40covers an upper surface of the piezoelectric film 33 to an end portionof the lower electrode 32 located beyond the piezoelectric film 33through the side surface 33 b, so that the piezoelectric film 33 may beprotected and further electrical insulation between the lower electrodes32 may increase.

<Individual traces 41>

As depicted in FIG. 5A, the individual trace 41 is disposed overlappingthe first exposed portion 32 c of the lower electrode 32. The individualtrace 41 is electrically connected to the lower electrode 32, via thefirst exposed portion 32 c. The individual trace 41 is formed of, forexample, gold (Au). The individual trace 41 is thicker than the lowerelectrode 32 and has a thickness of, for example, 1.0 μm.

As described above, an end portion of the conductive film 39 is thesecond exposed portion 39 a, which exposed from the insulating film 40.An end portion of the individual trace 41 overlaps the first exposedportion 32 c of the lower electrode 32 and the second exposed portion 39a of the conductive film 39.

FIG. 5B shows one of modification of the illustrative embodiment. Themodification includes an insulating film 60 instead of the insulatingfilm 40. In this modification, an insulating film 60 is disposed betweenthe individual trace 41 and conductive film 39. As depicted in FIG. 5B,if the insulating film 60 fully covers the conductive film 39 to its endportion, a portion of the first exposed portion 32 c located to theright of the conductive film 39 in FIG. 5B is directly covered by theinsulating film 60. In this modification, when the individual trace 41is laid on top of the first exposed portion 32 c, the portion of thefirst exposed portion 32 c directly covered by the insulating film 60has a minor portion that is out of contact with the conductive film 39or the individual trace 41. Especially, when the lower electrode 32 isthin, electrical disconnection may occur in the portion of the firstexposed portion 32 c. However, in an illustrative embodiment shown inFIG. 5A, the end portion of the conductive film 39 is exposed from theinsulating film 40. Therefore, reliability of electrical connection mayincrease as the individual trace 41 is laid over the second exposedportion 39 a of the conductive film 39 and the first exposed portion 32c of the lower electrode 32.

The individual trace 41 extends from a position above the piezoelectricfilm 33 along the first exposed portion 32 c of the lower electrode 32to a region between the two pressure chamber rows 28. A drive contact 46is formed at an end portion of the individual trace 41 opposite to thewide portion 32 a with respect to the scanning direction. Between thetwo pressure chamber rows 28, the drive contact 46 of the individualtrace 41 extending from the left piezoelectric element 31 and the drivecontact 46 of the individual trace 41 extending from the rightpiezoelectric element 31, alternates along the feeding direction.

<Common Trace 42>

The common trace 42 includes a thin trace 43 and a thick trace 44, eachdisposed at a different layer. The thin trace 43 and the thick trace 44are electrically connected to the upper electrodes 34.

As depicted in FIGS. 3 and 5, the thin trace 43 is disposed on an endportion of an upper surface of the piezoelectric body 37 in the scanningdirection. The thin trace 43 extends along the feeding direction. Endportions (e.g., a left end portion in FIG. 5A) of the upper electrodes34 aligned along the feeding direction are electrically connected toeach other by the thin trace 43. The thin trace 43 is formed of the samematerial as the upper electrodes 34 (e.g., iridium). The thin trace 43is provided on the same layer as the upper electrode 34. As will bedescribed later, the thin trace 43 may be formed at the same time as theprocess of patterning the upper electrodes 34.

The thick trace 44 is formed above the insulating film 40. As depictedin FIG. 2, the thick trace 44 encloses the upper electrodes 34 arrangedalong the feeding direction on an upper surface of the piezoelectricbody 37. Edge portions (e.g., left end portions in FIG. 5A) of the upperelectrodes 34 are electrically connected to each other by an end portionof the thick trace 44 in the scanning direction. Inner end portions(e.g., a right end portion in FIG. 5A) of the upper electrodes 34 in thescanning direction are electrically connected to each other by an innerportion of the thick trace 44 in the scanning direction. The thick trace44 is formed of the same material as the individual traces 41 (e.g.,gold). The thick trace 44 is thicker than the upper electrode 34, andhas a thickness of for example, 1.0 μm. As the upper electrodes 34 areelectrically connected by the thick trace 44, electric resistance of thecommon trace 42 may be reduced. This may reduce variances in thepotentials of the upper electrodes 34.

The individual traces 41 and the thick trace 44 of the common trace 42may be formed of material, e.g., aluminum, other than gold. When thetraces 41 and 44 are formed of aluminum, the traces 41 and 44 may bepreferably covered by a trace protective film formed of, for example,silicon nitride (SiN).

As depicted in FIGS. 2 and 3, the thin trace 43 and an end portion ofthe thick trace 44 in the scanning direction constitute a firstconnecting trace 45 a configured to electrically connect end portions ofthe upper electrodes 34 in the scanning direction. An inner portion ofthe thick trace 44 in the scanning direction constitutes a secondconnecting trace 45 b configured to electrically connect inner endportions of the upper electrodes 34 in the scanning direction.

The common trace 42 further includes overlapping portions that overlapend portions of the pressure chambers 26 in the scanning direction. Morespecifically, as depicted in FIGS. 3, 5A and 5B, a portion of the firstconnecting trace 45 a disposed on an end side of the head unit 16 in thescanning direction overlaps an end portion of the pressure chamber 26 inthe scanning direction. A portion of the second connecting trace 45 bdisposed on an inner side of the head unit 16 in the scanning directionoverlaps an inner end portion of the pressure chamber 26 in the scanningdirection. The overlapping portions, e.g., the first connecting traces45 a and the second connecting traces 45 b, overlap end portions of thelower electrode 32 in the scanning direction. Thus, the common trace 42overlaps end portions of the pressure chamber 26 in the scanningdirection, so that the physical size of the head unit 16 in the scanningdirection may be reduced.

The insulating film 40 is disposed between the overlapping portions,e.g., the first connecting traces 45 a and the second connecting traces45 b, and the piezoelectric film 33. In other words, the insulating film40 overlaps edge portions of the pressure chamber 26 in the scanningdirection. Accordingly, a curvature radius of a deformed shape of thepiezoelectric film 33 may become relatively great at a positioncorresponding to the edge portion of the pressure chamber 26.Accordingly, a crack in the piezoelectric film 33 may be prevented orreduced. Further, the insulating film 40 overlaps end portions of thelower electrode 32 in the scanning direction, so that a crack mayfurther be prevented or reduced.

As depicted in FIG. 2, the common trace 42 includes two lead-out traces48, each configured to electrically connect the second connecting traces45 b disposed on upper surfaces of the left and right piezoelectricbodies 37. Each of the lead-out traces 48 is disposed at a regionbetween the two pressure chamber rows 28, in front of and behind theplurality of drive contacts 46, e.g., in front of a frontmost drivecontact 46 and behind a rearmost drive contact 46. A central portion ofeach lead-out trace 48 in the scanning direction includes a groundcontact 47 to which the COF 50 (described below) is bonded.

(COF)

As depicted in FIGS. 2-5B, one end portion of the COF 50 is bonded to acentral portion of the channeled substrate 21 in the scanning directionwhere the drive contacts 46 and the two ground contacts 47 are disposed.The driver IC 51 is mounted to a portion of the COF 50. The other endportion of the COF 50 is connected to the controller 6 of the printer 1(refer to FIG. 1). The COF 50 includes a plurality of input traces 53, aplurality of output traces 52, and a ground trace (not depicted). Theinput traces 53 and the output traces 52 are connected to the driver IC51. The driver IC 51 is electrically connected to the controller 6 viathe input traces 53. When the COF 50 is bonded to the channeledsubstrate 21, an end of each output trace 52 is electrically connectedto a respective one of the drive contacts 46. The ground trace of theCOF 50 is electrically connected to the ground contacts 47.

The driver IC 51 is configured to generate drive signals, based oncontrol signals from the controller 6, and output the drive signals tothe piezoelectric elements 31. The drive signals are input to the drivecontacts 46 via the output traces 52, and supplied to the correspondinglower electrodes 32 via the individual traces 41. At this time, thepotential of the lower electrode 32 changes between a predetermineddrive potential and the ground potential. The ground potential isapplied to the upper electrodes 34 connected to the ground contacts 47.

Operations of the piezoelectric element 31 when a drive signal issupplied from the driver IC 51 will be described. When a drive signal isnot supplied, the potential of the lower electrode 32 is at the groundpotential, which is the same potential as that of the upper electrode34. As a drive signal is supplied to the lower electrode 32, an electricfield parallel to the thickness direction of the active portion 36 ofthe piezoelectric film 33 is applied to the active portion 36, due tothe potential difference between the lower electrode 32 and the upperelectrode 34. At this time, the active portion 36 above the insulatingfilm 30 deforms, and the piezoelectric element 31 as a whole convexlydeforms toward the pressure chamber 26. Thus, the volumetric capacity ofthe pressure chamber 26 is reduced and a pressure wave is generated inthe pressure chamber 26. Accordingly, an ink droplet is ejected from thenozzle 24 communicating with the pressure chamber 26.

(Cover Member)

The cover member 23 is provided to protect the piezoelectric elements31. The cover member 23 is attached to an upper surface of theinsulating film 30 with adhesive. As depicted in FIG. 5A, the covermember 23 includes an opening portion 23 a and a cover portion 23 b. Theopening portion 23 a is disposed at a central portion of the covermember 23 in the scanning direction. The cover portion 23 b is disposedon each left and right side of the opening portion 23 a. The COF 50bonded to the drive contacts 46 and the two ground contacts 47 isinserted into the opening portion 23 a. Each left and right coverportion 23 b covers a corresponding one of the two piezoelectric bodies37. The openings of the manifolds 25, each formed at a respective one ofleft and right end portions of the channeled substrate 21, are exposedfrom the cover member 23, to allow the ink supply member (not depicted)to be connected to the openings of the manifolds 25.

Next, manufacturing processes of the head unit 16 will be described.FIGS. 7A-7E depict manufacturing processes of the piezoelectric actuator22. FIG. 7A depicts a process of forming the insulating film 30. FIG. 7Bdepicts a process of forming the lower electrodes 32. FIG. 7C depicts aprocess of forming the piezoelectric film 33. FIG. 7D depicts a processof forming the upper electrodes 34. FIG. 7E depicts process of formingthe insulating film 40 for protecting the piezoelectric film 33.

First, as depicted in FIG. 7A, the insulating film 30 of silicon dioxideis formed on a surface of the silicon channeled substrate 21 by, forexample, thermal oxidation.

Next, as depicted in FIG. 7B, a film of, for example, a platinum (Pt),is formed on the insulating film 30, for example, by sputtering, and ispatterned to form the plurality of lower electrodes 32. At this time,the lower electrodes 32 are patterned such that, with respect to thefeeding direction, each end of the lower electrode 32 is located furtherfrom a corresponding end of a pressure chamber formation region C of thechanneled substrate 21 where the pressure chamber 26 is formed. In otherwords, the lower electrode 32 extends beyond each end of the region Cwith respect to the feeding direction.

Next, as depicted in FIG. 7C, the piezoelectric film 33 is formed, abovethe lower electrodes 32, of piezoelectric material, e.g., PZT, entirelyon the upper surface of the insulating film 30, for example, by asol-gel method or a spattering method. The piezoelectric film 33 ispatterned by etching to form the piezoelectric bodies 37.

With respect to the feeding direction, each end of the lower electrode32 is located further from a corresponding one of the two side surfaces33 b of the piezoelectric film 33. In other words, an entire portion ofthe piezoelectric film 33 is disposed above the lower electrode 32 withrespect to the feeding direction. Therefore, with respect to the feedingdirection, the piezoelectric film 33 may be formed on the same planarcondition. Accordingly, the crystal orientation direction of thepiezoelectric material constituting the piezoelectric film 33 may beuniform with respect to the feeding direction, and discontinuouscrystallinity may not occur.

The lower electrode 32 is formed above the insulating film 30 andextends beyond each end of the pressure chamber forming region C of thechanneled substrate 21 with respect to the feeding direction. When thepiezoelectric film 33 is patterned as described above, reduction in thethickness of a portion of the insulating film 30 covering the pressurechambers 26 may be prevented or reduced by the lower electrode 32.

Next, as depicted in FIG. 7D, a film of, for example, iridium (Ir), isformed on an upper surface of the piezoelectric film 33, for example, bya sputtering method. The iridium film is patterned to form the pluralityof upper electrodes 34. At this time, each upper electrode 34 is formedsuch that right and left ends of the upper electrode 34 in FIG. 7D islocated closer to the center of a corresponding pressure chamber 26 withrespect to the feeding direction than right and left ends of acorresponding lower electrode 32 in FIG. 7D, respectively. In otherwords, each end of the upper electrodes 32 with respect to the feedingdirection is located closer to the center of the pressure chamber 26with respect to the feeding direction than a corresponding end of thelower electrode 32. Thus, a position of each end of the active portion36 with respect to the feeding direction is determined by the positionof the upper electrode 34 with respect to the feeding direction. Asdescribed above, crystal orientation of the piezoelectric film 33disposed above the lower electrode 32 may be uniform. Therefore, endportions of the active portion 36 may not have discontinuouscrystallinity.

When the upper electrodes 34 are patterned as described above, theconductive film 39 (refer to FIG. 5A), which covers the upper surface ofthe piezoelectric film 33 to the first exposed portion 32 c of the lowerelectrode 32 via the side surface 33 a, is left, so that the firstexposed portion 32 c may be prevented or reduced from being etched. Thethin trace 43 of the common trace 42 (refer to FIGS. 3, 5A and 5B)configured to electrically connect the upper electrodes 34 is formed atthe same time when the upper electrodes 34 are patterned.

Next, as depicted in FIG. 7E, the insulating film 40 is formed on theupper electrodes 34, and is patterned. Although not depicted in FIG. 7E,the individual traces 41, and the thick trace 44 of the common trace 42(refer to FIG. 5A) are formed of, for example, gold (Au), on theinsulating film 40.

FIG. 8A depicts a process of forming the pressure chambers 26. FIG. 8Bdepicts a process of bonding the nozzle plate 20. After thepiezoelectric actuator 22 is formed, the cover member 23 (refer to FIG.5A) is bonded to the channeled substrate 21. Thereafter, the channeledsubstrate 21 is subjected to a polishing process. Thereafter, asdepicted in FIG. 8A, etching is performed from a lower surface of thechanneled substrate 21 opposite to the piezoelectric actuator 22, toform a plurality of the pressure chambers 26 on the channeled substrate21. Further, as depicted in FIG. 8B, the nozzle plate 20 is bonded tothe lower surface of the channeled substrate 21 opposite to thepiezoelectric actuator 22.

In the above-described illustrative embodiment, the longitudinaldirection of the pressure chamber 26. e.g., the scanning direction,corresponds to “a longitudinal direction” in the disclosure. Thetransverse direction e.g., the feeding direction, corresponds to “atransverse direction” in the disclosure. The head unit 16 corresponds to“a liquid ejection apparatus” in the disclosure. The wide portion 32 acorresponds to “a partial overlapping portion” in the disclosure. Theinsulating film 30 corresponds to “a first insulating film” in thedisclosure. The insulating film 40 corresponds to “a second insulatingfilm” in the disclosure. The thick trace 44 corresponds to “a firstconductive layer” in the disclosure. The thin trace 43 corresponds to “asecond conductive layer” in the disclosure.

Next, modifications of the above-described illustrative embodiment willbe described. Like reference numerals denote like corresponding partsand detailed description thereof with respect to the followingmodifications will be omitted herein.

1] The following modification may be made as long as, with respect tothe feeding direction, each end of the upper electrode 34 is locatedcloser to the center of the pressure chamber 26 than a corresponding endof the lower electrode 32.

For example, as depicted in FIG. 9A, with respect to the feedingdirection, each end of the lower electrode 32 may be located closer tothe center of the pressure chamber 26 than a corresponding end of thepiezoelectric film 33. Alternatively, as depicted in FIG. 9B, withrespect to the feeding direction, each end of the lower electrode 32 maybe located closer to the center of the pressure chamber 26 than acorresponding end of the pressure chamber 26.

In the structures of FIGS. 9A and 9B, each end of the lower electrode 32is closer to the center of the pressure chamber 26 than a correspondingend of the piezoelectric film 33 with respect to the feeding direction.This may cause discontinuous crystallinity at a position between aparticular portion of the piezoelectric film 33 above the lowerelectrode 32 and another portion further from an end of the particularportion with respect to the feeding direction. However, each end of theupper electrode 34 is located closer to the center of the pressurechamber 26 than a corresponding end of the lower electrode 32 withrespect to the feeding direction. Therefore, with respect to the feedingdirection, positions of ends of the active portion 36 are determined bypositions of the ends of the upper electrode 34. The ends of the lowerelectrode 32 are irrelevant to define the active portion. In otherwords, even when the piezoelectric film 33 has a discontinuous portionwith respect to crystallinity, at the end of the lower electrode 32, thediscontinuous portion may not at an end portion of the active portion36. Accordingly, occurrence of a crack in the piezoelectric film 33 whenthe active portion 36 deforms may be prevented or reduced.

2] In the illustrative embodiment, as depicted in FIG. 6, the slit 38 isprovided at a position between the two pressure chambers 26 adjacentalong the feeding direction. In another embodiment, the slit 38 may notnecessarily provided and the piezoelectric film 33 may continue betweenadjacent pressure chambers 26 with respect to the feeding direction, asdepicted in FIG. 10.

3] In the illustrative embodiment, the conductive film 39 is provided atthe side surface 33 a of the piezoelectric film 33 through which thelower electrode 32 is exposed. In another embodiment, the conductivefilm 39 may be omitted.

4] A position where the insulating film 40 is formed for covering thepiezoelectric film 33, may be changed as necessary. For example, in theillustrative embodiment, the insulating film 40 overlaps, with respectto the scanning direction, an edge portion of the pressure chamber 26and the active portion 36, as depicted in FIG. 5A. In anotherembodiment, the insulating film 40 may not necessarily overlap theactive portion 36. The insulating film 40 may be formed on thepiezoelectric film 33 at a position further from an edge of the pressurechamber 26 with respect to the scanning direction, without overlappingthe edge portion of the pressure chamber 26.

As depicted in FIG. 11, a right end portion of the insulating film 40may not necessarily cover the conductive film 39. Alternatively, asdepicted in FIG. 12, a portion of the insulating film 40 between theconductive film 39 and the thick trace 44 may be removed, after theinsulating film 40 covers the conductive film 39.

5] The structure of the common trace 42 may be changed as necessary. Forexample, as depicted in FIG. 13, a left portion of the thick trace 44may contact the plurality of upper electrodes 34 (only one of which isdepicted in FIG. 13) or the thin trace 43 at a region further from edgesof the pressure chambers 26 (only one of which is depicted in FIG. 13)with respect to the scanning direction. The common trace 42 may notnecessarily include two types of traces 43 and 44, each provided at adifferent layer, but may include one type of the traces 43 and 44. Thecommon trace 42 may not necessarily overlap end portions of theplurality of pressure chambers 26 in the scanning direction. The commontrace 42 may not necessarily overlap the pressure chambers 26.

In the illustrative embodiment and its modifications, the disclosure isapplied to an inkjet head configured to eject ink on a recording sheetto print, for example, an image. The disclosure may be applied to aliquid ejection apparatus to be used in various applications other thanan image printing. For example, the disclosure may be applied to aliquid ejection apparatus configured to eject conductive liquid on asubstrate to form conductive patterns on a surface of the substrate.

What is claimed is:
 1. A liquid ejection apparatus, comprising: apressure chamber having a longitudinal direction; a first insulatingfilm covering the pressure chamber; a piezoelectric elementcorresponding to the pressure chamber and including a lower electrodedisposed above the first insulating film, a piezoelectric film disposedabove the lower electrode, and an upper electrode disposed above thepiezoelectric film; a common trace connecting to the upper electrode andanother upper electrode, the upper electrode and the another upperelectrode are disposed side by side in a transverse direction, thetransverse direction is orthogonal to the longitudinal direction; andwherein the lower electrode has a partial overlapping portion and anon-overlapping portion; the partial overlapping portion at leastpartially overlaps the pressure chamber in an orthogonal direction, theorthogonal direction is orthogonal to the longitudinal direction and thetransverse direction; the partial overlapping portion of the lowerelectrode has two ends in the transverse direction; the upper electrodehas two ends in the transverse direction; and a distance from the centerof the pressure chamber in the transverse direction to one of the twoends of the upper electrode in the transverse direction is smaller thana distance from the center of the pressure chamber in the transversedirection to a corresponding one of the two ends of the partialoverlapping portion in the transverse direction.
 2. The liquid ejectionapparatus according to claim 1, wherein a distance from the center ofthe pressure chamber in the transverse direction to the other of the twoends of the upper electrode in the transverse direction is smaller thana distance from the center of the pressure chamber in the transversedirection to a corresponding the other of the two ends of the partialoverlapping portion in the transverse direction.
 3. The liquid ejectionapparatus according to claim 1, wherein the lower electrode includes aplatinum layer.
 4. The liquid ejection apparatus according to claim 1,further comprising a seed layer between the lower electrode and thepiezoelectric film.
 5. The liquid ejection apparatus according to claim1, wherein the pressure chamber has two ends in the transversedirection; a distance from the center of the pressure chamber in thetransverse direction to the one of the two ends of the partialoverlapping portion of the lower electrode in the transverse directionis greater than a distance from the center of the pressure chamber inthe transverse direction to a corresponding one of the two ends of thepressure chamber in the transverse direction.
 6. The liquid ejectionapparatus according to claim 1, wherein the piezoelectric film has a topsurface, a bottom surface and two side surfaces, each of the two sidesurfaces extends from the top surface to the bottom surface; and the twoside surfaces are located on opposite sides of the center of thepressure chamber in the transverse direction.
 7. The liquid ejectionapparatus according to claim 6, further comprising a second insulatingfilm covering at least a portion of the top surface of the piezoelectricelement, the two side surfaces of the piezoelectric film, and the twoends of the partial overlapping portion of the lower electrode in thetransverse direction, wherein the two ends of the partial overlappingportion of the lower electrode in the transverse direction are locatedat outside of the piezoelectric film in the transverse direction.
 8. Theliquid ejection apparatus according to claim 1, further comprising asecond insulating film covering at least a portion of a top surface ofthe piezoelectric element.
 9. The liquid ejection apparatus according toclaim 8, wherein the pressure chamber has an end in the longitudinaldirection; the pressure chamber extends from the end of the pressurechamber towards a first direction, the first direction is in thelongitudinal direction; the second insulating film has an end in thelongitudinal direction; the second insulating film extends from the endof the second insulating film towards a second direction opposite to thefirst direction, the second direction is in the longitudinal direction;the second insulating film extends towards the second direction beyondthe end of the pressure; and a distance from the center of the pressurechamber in the longitudinal direction to the end of the secondinsulating film in the longitudinal direction is smaller than a distancefrom the center of the pressure chamber in the longitudinal direction tothe end of the pressure chamber in the longitudinal direction.
 10. Theliquid ejection apparatus according to claim 9, wherein the upperelectrode has an end in the longitudinal direction; the upper electrodeextends from the end of the upper electrode towards the first direction;the second insulating film disposed over a portion of the upperelectrode, where the portion is proximate the end of the upperelectrode; the second insulating film extends toward the seconddirection beyond the end of upper electrode; and a distance from thecenter of the pressure chamber in the longitudinal direction to the endof the second insulating film in the longitudinal direction is smallerthan a distance from the center of the pressure chamber in thelongitudinal direction to the end of the upper electrode in thelongitudinal direction.
 11. The liquid ejection apparatus according toclaim 9, further comprising an individual trace connected to the lowerelectrode; wherein the lower electrode includes an exposed portion; thepiezoelectric film and the second insulating film are absent over theexposed portion; and the individual trace is connected to the lowerelectrode at the exposed portion.
 12. The liquid ejection apparatusaccording to claim 11, further comprising a conductive film formed of asame material as the upper electrode; and wherein the individual traceis connected to the lower electrode via the conductive film.
 13. Theliquid ejection apparatus according to claim 9, wherein a width of thepartial overlapping portion in the transverse direction is a greaterthan a width of the non-overlapping in the transverse direction; thepartial overlapping portion has an end in the longitudinal direction;the partial overlapping portion extends from the end of the partialoverlapping portion towards the first direction; the second insulatingfilm extends towards the second direction beyond the end of the partialoverlapping portion.
 14. The liquid ejection apparatus according toclaim 1, wherein the common trace including a first conductive layerthat is thicker than the upper electrode.
 15. The liquid ejectionapparatus according to claim 14, wherein the common trace including asecond conductive layer that is same layer as the upper electrode.
 16. Amethod for manufacturing a liquid ejection apparatus comprising; forminga first insulating film over a substrate; forming a lower electrodehaving two ends thereof in particular direction over the firstinsulating film; forming a piezoelectric film over the lower electrode;and forming a upper electrode and common trace over the piezoelectricfilm, the upper electrode having two ends thereof in the particulardirection and, the common trace connects to the upper electrode andanother upper electrode; and, wherein a distance from a center of theupper electrode in the particular direction to one of the two ends ofthe upper electrode in the particular direction is smaller than adistance from the center of the lower electrode in the particulardirection to a corresponding one of the two ends of the lower electrodein the particular direction.
 17. A liquid ejection apparatus,comprising: a pressure chamber having a longitudinal direction; aninsulating film covering the pressure chamber; a piezoelectric elementcorresponding to the pressure chamber and including a lower electrodedisposed above the insulating film, a piezoelectric film disposed abovethe lower electrode, and an upper electrode disposed above thepiezoelectric film; a common trace connecting to the upper electrode andanother upper electrode; and, wherein the lower electrode has two endsin a transverse direction, the transverse direction is orthogonal to thelongitudinal direction; the two ends of the lower electrode are locatedon opposite sides of a center of the pressure chamber in the transversedirection; the upper electrode has two ends in the transverse direction;the two ends of the upper electrode are located on opposite sides of thecenter of the pressure chamber in the transverse direction, and; asviewed along a centerline of the pressure chamber extending in thetransverse direction, a distance from the center of the pressure chamberin the transverse direction to one of the two ends of the upperelectrode in the transverse direction is smaller than a distance fromthe center of the pressure chamber in the transverse direction to acorresponding one of the two ends of the lower electrode in thetransverse direction.